I'm working at a company that uses lots of Perl that's not exactly a startup, but it's still a young company. Sure, we use some PHP and Python as well, but Perl's a vital part of the software code base.

My guess is that 'new' companies sell themselves as using 'new' technology (for some definition of 'new') in order to present themselves as 'cutting edge'. But I think Marc Andreesen has really nailed it in this blog post of his: the only thing that really matters is pressure from the market to provide a good or service that it wants. The technology that it's built on is secondary, tertiary or plain Just Doesn't Matter.